Technical Field
[0001] The invention relates to monoclonal antibodies and to techniques for imaging desired
target tissue to permit its precise localization. In particular, this invention relates
to identifying the location of parathyroid tissue using antibodies, and to the therapeutic
use of these antibodies.
Background Art
[0002] An estimated 250.000 people in the United States exhibit abnormally high secretion
of parathyroid hormone, an 84-amino acid linear peptide which is involved in regulating
the concentration of calcium ion in the plasma. The hormone apparently acts by regulating
bone resorption and tubular reabsorption of calcium and phosphorus in the kidney.
In primary hyperparathyroidism, tissue calcium storage is decreased, and bone demineralization
results. Generally, hyperparathyroidism is the result of tumor formation in the parathyroid
glands, four small egg-shaped glands closely associated with the thyroid.
[0003] The standard treatment for hyperparathyroidism is surgical removal of all abnormally
enlarged glands. To do so successfully, however, requires that they be precisely located.
They are notoriously difficult to locate, and even after surgery, symptoms may persist
due to failure to remove hyperfunctioning parathyroid tissue completely.
[0004] While the approximate location of the parathyroids is presumed known, precise location
is not established, and, further, these glands may be ectopic in various locations
in the neck, throat and chest region. Therefore, an imaging technique which would
permit the surgeon to establish the location of parathyroid tissue either in normal
locations or ectopic placements is highly desirable. Such techniques are not presently
available in the art.
[0005] Substances specific for parathyroid tissue are useful for development of such techniques.
Antibodies, if properly chosen, show the necessary specificity. Monoclonal antibodies
reactive with parathyroid tissue have been used to modulate the secretory function
(Posillico, J.T., et al, Clin Res (1985) 33:473A. However, these antibodies may not
be suitable for imaging.
Disclosure of the Invention
[0006] The invention provides a highly specific imaging technique for visualizing the parathyroid
glands prior to surgery. The technique employs a labeled monoclonal antibody preparation
which is highly immunoreactive with an antigen associated with parathyroid tissue
and which antibody preparation does not react with other types of cells. Administration
of this labeled monoclonal antibody prior to surgery permits imaging of the neck,
throat and chest area to obtain a clear picture of the location of parathyroid tissue.
[0007] In addition, the antibodies of the invention stimulate the secretion of parathyroid
hormone and are thus useful in treating patients who exhibit a deficiency in the ability
to secrete this hormone, they can also be conjugated to toxic moieties in order to
form immunotoxins therapeutically useful in treating hyperplasia of the parathyroid
gland.
[0008] In one aspect, the invention is directed to monoclonal antibody preparations useful
in radioimaging parathyroid tissue. These monoclonal antibodies are specifically reactive
with parathyroid tissue to the exclusion of other types, and include monoclonals of
the IgM class, but for use in this purpose are preferably preparations comprising
IgG antibodies. The invention further includes these antibodies in labeled form. For
use in treating hypoparathyroidism. antibodies of class IgM are preferred. Either
class may be employed to form immunotoxins. In addition, for use in radioimaging and
in the preparation of immunotoxins, fragments of the antibodies which retain antigen
specificity may be employed. Accordingly, the Fab or F(ab')
2 fragments may also be used for this purpose.
[0009] In another aspect, the invention is directed to immortalized cell cultures capable
of producing the antibodies of desired specificity. In still another aspect, the invention
relates to radioimaging techniques using the antibodies of the invention, to methods
of treating hypoparathyroidism with the parathyroid-specific monoclonal antibodies
and to methods of treating hyperparathyroidism using immunotoxins prepared from the
antibodies of the invention.
Brief Description of the Drawings
[0010]
Figures 1 and 2 are photomicrographs, taken in opposite phases, of parathyroid transplants
in nude mice after the mice were injected with BB5-G1 conjugated to 1-125 .
Figure 3 shows the time dependence of PTH secretion stimulation by the monoclonal
antibodies of the invention.
Figure 4 shows the dose-response curve for acutely dispersed bovine parathyroid cells
treated with BB5-M antibodies.
Figure 5 shows the effect of BB5-M antibody treatment on the secretion of intact parathyroid
hormone (PTH) and of the C-terminal fragment containing amino acids 35-84 of PTH.
Modes of Carrying Out the Invention
A. Definitions
[0011] Antibodies "specifically immunoreactive" with a particular antigen refers to the
ability to react positively with the antigen to the exclusion of others. It is recognized
that at high enough concentration, immunoglobulins in general will bind to substrates
nonspecifically. However, this nonspecific binding can be discerned by diluting the
sample appropriately and comparing the effects of this dilution to dilutions of a
specifically reacting antibody.
[0012] A "parathyroid-characteristic antigen" refers to a substance which contains an antigenic
determinant found exclusively on parathyroid tissues and not on other tissues derived
from the same organism.
[0013] The "191 kd" antigen refers to an antigen specifically associated with parathyroid
tissue which binds to a specific monoclonal antibody preparation herein (BB5). This
antigen shows a molecular weight on SDS-PAGE run in the absence of 2-mercaptoethanol
(BME) of 191 kd; in the presence of BME, the apparent molecular weight is 171 kd.
The antigen is associated with the parathyroid cell surface and is apparently not
secreted.
[0014] "Cells", "cell line", and "cell cultures" are generally used interchangeably, unless
otherwise specified, and these terms include but are not limited to individual cells,
harvested cells, cultures containing cells, and so forth. Furthermore, a particular
designation includes the progeny of that originally prepared. It is understood that
spontaneous or induced changes can take place in the DNA and morphology of cells over
several generations. Progeny which contain such changes are still included within
the definition so long as their essential features as related to the invention are
maintained. For example, for a hybridoma secreting the monoclonal antibody specific
against parathyroid tissue, any descendant of a secreting cell originally identified
is included so long as it continues to secrete the antibody with desired characteristics.
[0015] For convenience, clones of immortalized cells and the monoclonal antibodies they
secrete will be designated by the same name -- for example, BB5-M refers both to the
antibody and to the cells secreting it.
[0016] "Immortalizing cell line" refers to a cell line which can be perpetually (for practical
purposes) maintained in cell culture, that is, for an indefinite number of transfers.
It also confers this property on the fusion product when fused to an ordinary nontransformed
cell line.
B. General Description
[0017] Disclosed below are procedures for preparation of monoclonal antibodies specifically
immunoreactive with human parathyroid-characteristic antigens, for labeling these
antibodies, and for using these labeled antibodies to locate parathyroid tissue in
human subjects. Also described are methods of treating
hypoparathyroidism by administering the antibodies of the invention, and of treating
hyperparathyroidism by administering immunotoxins prepared from these antibodies.
Preparation of Monoclonal Antibodies
[0018] In general, the procedure of Kohler and Milstein is adapted to the preparation of
the desired antibodies and, if desired, followed by obtaining appropriate switch variants
using the method of Dangl, J.L., and Herzenberg, L.A., J Immunol Meth (1982) 52:1.
[0019] Hybridomas capable of secreting the desired monoclonal antibodies are created by
fusing spleen cells or peripheral blood lymphocytes from a mammal immunized with parathyroid
tissue to cells of an immortalizing cell line, typically a myeloma line of the same
species as that from which the antibody-secreting cell is derived. Convenient myeloma
lines are available from mouse and rat, and these mammals therefore make good subjects
for production of polyclonal antisera and the immunoglobulin-secreting cells. However,
it is understood that any available immortalizing cell line may be used with secreting
cells obtained from a compatible species. In addition, certain antibody-secreting
cells may be immortalized by viral infection, such as by treating with Epstein-Barr
virus. These alternate immortalizing techniques may also be employed to obtain the
immortalized immunoglobulin-secreting cells of the invention.
[0020] Hybridomas are created by fusing the antibody-secreting cell line with the immortalizing
cell line in the presence of an activating agent such as polyethylene glycol. Details
of this, now standard, procedure are known in the art and need not be recited here.
The critical parameters determining success or failure generally relate to the choice
of immortalizing cell lines or method of immortalizing, and to the choice of the population
of antibody-producing cells. This latter preparation is, in turn, dependent on the
use of the correct immunizing agent for administration to the mammal generating these
cells.
[0021] In the present invention, homogenates of parathyroid tissue obtained from patients
with primary parathyroid hyperplasia are appropriate. The parathyroid tissue is initially
physically separated from surrounding foreign contaminating tissue and homogenized
in phosphate buffered saline (PBS). The homogenate is then emulsified in Freund's
complete adjuvant and injected into suitable host organisms, preferably mice.
[0022] In a preferred procedure, isolated spleen cells from the immunized mice are fused
with a myeloma line derived from the same species, and the resulting cells grown on
selective media. Many readily available myeloma lines are HAT or AH sensitive, that
is, they fail to grow on a medium containing hypoxanthine, aminopterin, and thymidine,
or on AH medium containing azaserine and hypoxanthine. Both of these media take advantage
of the capacity of normal cells to utilize a salvage pathway for DNA synthesis under
circumstances where the de novo process is inhibited (in this case, by aminopterin
or azaserine). Hypoxanthine and thymidine (or hypoxanthine alone) are requirements
for the salvage pathway.
[0023] Therefore, only immortalizing cells which are fused to normal cells are capable of
survival in this selection medium: unfused immortalizing cells which are HAT or AH
sensitive will die. Of course, the normal cells which have not been immortalized by
fusion would
die anyway. Therefore, only cultures containing fused cells are ultimately available
for screening to detect production of the desired antibody.
[0024] Cultures of fused cells which survive in selection medium or cells immortalized by
other methods are then screened for secretion of antibody having the desired characteristics.
The culture media are assayed using immunoreaction-based assays, including, without
limitation, Western blot, ELISA, and RIA. The antigen used for this screen must be
chosen to insure the correct specificity. Useful in this regard are purified parathyroid
homogenates or sections of parathyroid tissue, including those of other species which
are suitably cross-reactive. Particularly desirable is screening with the herein-identified
parathyroid-characteristic antigen of molecular weight 191 kd. Negative screens are
also included to insure parathyroid specificity.
[0025] The antibodies from a line identified as secreting the correct antibodies can be
recovered from the medium using standard purification techniques if desired. Standard
techniques are also available for labeling the isolated antibodies.
[0026] For use in the radioimaging method of the present invention, it is desirable to obtain
monoclonal antibodies of a class capable of passing through the vascular walls. In
the illustration below, the cell line identified initially as secreting the antibodies
of desired specificity produced antibodies of class IgM, a pentamer which may cause
difficulty in in vivo use due to its relative inability to cross the vascular walls
of the circulation system. For such use, it would be preferable to obtain this immunoglobulin
in monomeric form. Also, if to be used therapeutically, the functional characteristics
of other subclasses may be desired. Techniques for obtaining switch variants are available,
as described by Dangl and Herzenberg (supra). These techniques capitalize on the lack
of complete monoclonal character of a particular set of progeny from a single ancestor,
a consequence of the spontaneous mutation which occurs in the process of cell division
at very low frequency, sufficient to generate about 1 descendant out of 10 cells,
which, in fact, produces a different class of immunoglobulin. Obtaining "switch variants"
is really a process of repeatedly screening populations for the few cells which have
the desired property.
[0027] In a typical procedure to identify these populations, the hybridoma secreting the
surface immunoglobulin of desired specificity is stained with a fluoresceinated or
otherwise labeled antiserum specific for the desired isotype. The cells are then sorted
on a fluorescence-activated cell sorter (FACS) and the brightest 0.5-1% of the cells
are chosen. The dead cells must be gated out with propidium iodide to avoid selecting
nonspecifically fluorescent cells. The sorted population is then grown in tissue culture
and sorted in the same way to enrich for cells expressing the desired isotype. Several
rescreenings may be required to obtain an identifiable population of cells secreting
the correct isotype. Cells are cultured from this identified subtype and used to obtain
individual colonies.
[0028] The selected and screened hybridomas that produce the desired antibodies are grown
in vitro or in vivo using standard procedures. The antibodies are isolated from culture
media or body fluids, as the case may be, by conventional immunoglobulin purification
procedures such as ammonium sulfate precipitation, gel electrophoresis, dialysis,
chromatography and ultrafiltration to a purity appropriate to the expected use.
[0029] If antigen-specific fragments are desired for use in radioimaging or immunotoxin
preparation, the Fab or F(ab
l)
2 fragments may be prepared by standard methods such as those described by Weir, D.M.,
Handbook of Experimental Immunology (3d Ed, 1978) Blackwell Science Publ.. Oxford.
Use of Labeled Monoclonal Antibodies in Imaging
[0030] Labeled monoclonal preparations are useful in locating parathyroid tissue in candidates
for parathyroidectomy. Techniques for labeling antibodies or their subfragments are
well known in the art, and a variety of labels are used, depending on the purposes
for which the immunoglobulins are intended, including fluorescent, chromogenic, and
radioactive labels. Typically, for in vivo applications radiolabeled antibodies are
preferred, as this permits detection of the internalized antibodies.
[0031] A number of radioisotopes are commonly used, including iodine-123, iodine-125, iodine-131,
technetium-99, gallium-67, and indium-111. The iodine isotopes are not preferred because
they interact with the thyroid gland and may exhibit side effects, although otherwise
they are satisfadtory. Technetium-99 has a half life of approximately six hours, which
is difficult to accommodate to some purposes, and, in particular, may require for
use in the method of the invention levels of radiation which are higher than desired.
Indium-111, on the other hand, has a half life of three days and appears to be the
preferred isotope.
[0032] Methods for binding these isotopes to the antibody or a fragment of antibody are
understood in the art and include the use of iodination with 1, 3, 4, 6-tetrachloro-3a,
6a- diphenylglycocuril (Fraker,
P.J., et al, Biochem Biophys Res Comm (1978) 80:849-857) and the covalent coupling
of a chelating agent capable of binding metal ions such as indium-111, as described
by Hnatowich. D.J., et al, Science (1983) 220:613-615. The Hnatowich article contains
references to still other approaches to labeling proteins. Of course, other iodinating
and chelating methods can be used to attach the foregoing isotopes to the antibody
or fragment thereof.
[0033] The labeled monoclonal preparation is administered to the patient intravenously in
an appropriate carrier at a time several hours to 4 days before the tissue is to be
imaged. During this period. non-bound fractions are cleared from the body, and the
only remaining labeled monoclonal antibodies are those associated with the parathyroid
tissue. At this time, the subject is placed in front of a suitable gamma camera to
detect the presence of the isotope. This results in
3 "picture" of the labeled tissue, which can be correlated with known markers on the
patient's body to pinpoint the location of the parathyroid for the surgeon.
Use of Monoclonal Antibodies in Treatinq Parathyroid Secretion Abnormalities
[0034] The antibody preparations of the invention are also useful in directly treating patients
who have abnormally high or low levels of parathyroid hormone in their systems. Certain
of the antibodies per se are capable of effecting increased secretion of parathyroid
hormone upon binding to the gland. Conversely, tnese and other parathyroid-specific
antibodies, as well as antigen-specific fragments of these antibodies may also be
conjugated to toxic moieties such as, for example, ricin A, diphtheria toxin, abrin,
modeccin or bacterial toxins from Pseudomonas or Shigella. Toxins and their derivatives
have been utilized to form conjugates with antibodies specific to particular target
tissues, often cancer or tumor cells in order to obtain specific toxicity. See, for
example, Moolten, F.L., et al, Immun Rev (1982) 62:47-72 and Bernhard, M.I., Cancer
Res (1983) 43:4420. In addition, certain subclasses such as IgG2a and IgG2b are relatively
cytotoxic per se.
[0035] Conjugation of the toxic and parathyroid specific moieties can be conducted by standard
means known in the art. A number of commercially available bifunctional linking agents
are available, for example. from Pierce Chemical Company. Rockford, IL. Such crosslinking
agents include, most prominantly. heterobifunctional linkers such as N-succinimidyl3-(2-pyridyldithio)propionate
(SPDP) which generates a disulfide linkage at one terminus and an amide linkage with
an available amino group on the subject molecule at the other. A number of maleimido
containing compounds are also available which generate thioethers with available sulfhydryls
on the subject molecule, along with an amide at the other terminus, for example, succinimidyl4-(N-maleimidomethyl)cyclo-hexane-l-carboxylate
(SMCC). A large number of homobifunctional and heterobifunctional linkers are available
and methods for their use are understood in the art.
[0036] Administration of the antibodies or immunotoxins for therapeutic use is most conveniently
by an intravenous route, although by proper formulation, additional routes of administration
such as intraperitoneal, oral, or transdermal administration may also be used. Methods
of formulating compositions for administration to human subjects by an appropriate,
selected mode of administration are well understood in the art. For intravenous administration,
injectables can be prepared in conventional forms as liquid solutions or suspensions
or in solid forms suitable for solution or resuspension prior to injection, or as
emulsions. Suitable excipients include, for example, water, saline, dextrose, glycerol.
ethanol, Hank's solution. Ringer's solution and the like. In addition these compositions
may also contain minor amounts of non-toxic auxiliary substances such as wetting or
emulsifying agents. pH buffering agents, and so forth, such as sodium acetate, sorbitan
monolaurate, or triethanolamine oleate.
[0037] Antibodies useful for enhancing secretion of PTH are those which bind to the 191
kd parathyroid-characteristic antigen. Both BB5-G1 and BB5-M may be used and are preferred.
A suitable dosage is in the range of 50 µg - 1 mg. Repeated administrations may be
necessary, and therefore formulations suitable for self-administration may be desirable.
[0038] Administration of the immunotoxins to control hyperparathyroidism uses dosage levels
dependent on the toxicity of the conjugated toxin but will generally be in the range
of 0.1-1 mg/kg. The immunotoxin will generally be formulated into vehicles for parenteral
administration, such as Hank's solution or Ringer's solution in concentrations of
about 1 mg/ml to 10 mg/ml to permit the injection of relatively small volumes. Treatment
of patients for hyperparathyroidism using these materials will generally be on an
acute rather than on a chronic basis, and intravenous injection is entirely satisfactory
for this purpose.
Kits
[0039] The labeled antibody reagent may be packaged in unit dosage form, including means
for administration, such as an injection syringe, if desired.
[0040] The unlabeled materials used for direct treatment may also be packaged as kits. In
particular, the antibody preparation utilized for inducing increased secretion of
parathyroid hormone can be packaged in daily or weekly dosage units in suitable pharmaceutical
compositions for self-administration.
C. Examples
[0041] The following examples are intended to illustrate but not limit the invention.
Example 1
Preparation of Hybridoma BB5
[0042] Adult Balb/C mice were immunized intraperitoneally with a homogenate of parathyroid
tissue which had been obtained from patients with primary parathyroid hyperplasia,
separated from surrounding tissue, homogenized in PBS, and emulsified in Freund's
complete adjuvant. Several days later, the mice were sacrificed, and the spleen cells
fused with the non-secreting mouse myeloma line SP-2/0-Agl4 using the standard techniques
of Kohler and Milstein. After growth on HAT selective media, supernatants from the
hybridoma cultures were screened for parathyroid binding using a standard indirect
immunofluorescence assay. The assay employs frozen sections of human parathyroid glands
which had been cut into 0.2 u sections and immediately fixed in absolute alcohol.
The sections were incubated with supernatant, washed, and then incubated with a mixture
of goat anti-mouse IgM and goat anti-mouse IgG. which antibodies had been conjugated
with fluoroscein isothiocyanate (FITC). The sections were examined microscopically
for fluorescence binding.
[0043] Cultures with supernatants which bind specifically to the parathyroid tissue were
cloned in soft agar and retested using the parathyroid sections and negative screens
with sections of thyroid and tonsil.
[0044] In more detail, the alcohol treated sections were incubated for 30 min at 4°C with
1:10 dilutions of hybridoma supernatant, washed, and incubated for 30 min at 4°C with
a 1:50,dilution of the FITC conjugated goat anti-mouse antibodies (Tago, Inc.). The
sections were washed again, and examined with a fluorescence microscope.
[0045] Hybridoma BB5-M supernatant binds parathyroid tissue sectioned in this way but does
not bind to sections of thyroid or tonsil. The BB5-M cell line was cloned several
times in soft agar and the antibody was produced by culturing in serum-free medium.
The antibody was shown to be IgM (see below) and was purified by subjecting the supernatant
to affinity chromatography using Sepharose 4B coupled to M58.6, a rat anti-mouse IgM
monoclonal antibody to obtain a 90-95% pure preparation, as determined by SDS-PAGE.
Example 2
Characterization of BB5-M Antibody
[0046] The secreted antibodies from BB5-M media bound each of 15 different human parathyroid
frozen section specimens tested and four preparations of dispersed human parathyroid
cells. They cross-reacted with rhesus monkey, pig-tail monkey, and mongrel dog parathyroid
tissue, weakly with bovine parathyroid tissue, and not at all with rabbit or rat parathyroid
glands. The specificity of BB5-M for human parathyroid appears complete: cross-reactivity
was not obtained for any other tissue tested. Tissues tested include human thyroid,
tonsil, thymus, lymph nodes, spleen, salivary gland, adrenal gland, pancreas, islets,
pituitary gland, testis, pineal gland, pheochromocytoma, esophagus, liver, kidney,
lung, heart atrium, heart ventricle, gall bladder, duodenum, gastric antrum, cerebrum,
cerebellum, spinal cord, and hypothalamus, most of the same tissues in monkeys, and
thyroid and lymph node tissues from dogs.
[0047] The isotype was determined to be IgM.k by radioimmunoassay, described by Perlmutter,
R.M., et al, J Immunol (1978) 121:566.
Example 3
Antigen Characterization
[0048] The antigen to which BB5-M antibody was bound was identified by Western blot and
by subjecting an immunoprecipitated homogenate of surface
125I-labeled parathyroid tissue to SDS-PAGE and autoradiography.
[0049] Parathyroid tissue was obtained from patients with primary parathyroid hyperplasia,
and the tissue was minced and digested with collagenase/DNase as described by Brown,
B.M., et al, Endocrinol (1976) 99:1582. The dispersed cells were cultured for 48-72
hours to allow regeneration of any cell surface determinants which were removed during
digestion, since protease impurities in the collagenase preparation may cause digestion.
The cells were then surface-iodinated according to the method of Markwell, M.A.K..
et al, Biochem (1978)
17:807. The cells were lysed and the cell surface macromolecules immunoprecipitated
with BB5-M which had been indirectly coupled to staphylococcus with a rabbit anti-mouse
IgM antiserum. The immunoprecipitate was then analyzed on SDS-PAGE and autoradiographed.
[0050] Under non-reducing conditions, the major species immunoprecipitated with BB5-M migrated
as a 191 kd single polypeptide protein with two minor single-stranded precipitated
proteins of 162 kd and 129 kd. Under reducing conditions (BME) the protein migrated
as corresponding 171 kd, 140 kd, and 110 kd bands. The antigens precipitated do not
appear to be secreted by the target cells; BB5-M thus binds to a protein permanently
associated with the gland.
Example 4
Preparation of IgG
[0051] Using the method of Dangl and Herzenberg (supra), a switch variant was obtained from
BB5-M which secretes an IgGI antibody specific against parathyroid tissue. This hybridoma/immunoglobulin
was designated BB5-G1. The specificity of this variant was confirmed in a manner described
in Example 2 above. The Ig
Gl antibody was purified from the supernatant by affinity chromatography using Sepharose
4B coupled to 187.1, a rat anti-mouse
K light chain monoclonal antibody.
Example 5
Radiolocalization Studies of Parathyroid Implants in Nude Mice
[0052] Fresh parathyroid tissue obtained from patients undergoing parathyroidectomy was
minced and implanted into the posterior thigh muscles of nude Balb/C mice obtained
from Sasco. Inc., O'Fallon. MO and from St. Louis Children's Hospital, St. Louis,
MO using microsurgical techniques. Control human thyroid tissue or breast tissue was
transplanted into the contralateral thigh. After 2-3 weeks to allow the parathyroid
tissue to form a neovasculature, the mice were injected with purified radiolabeled
BB5-G1.
General Method
[0053] Mice containing the implants were injected with
125I-labeled BB5-G1. At various times, the mice were sacrificed and the grafts removed,
weighed, and counted to determine the percent of injected dose per gram of tissue
in the implant (% ID/gm). Some implants were fixed, sectioned, and autoradiographed
by dipping the slides in photographic emulsion. After several days exposure, the slides
were developed, stained with eosin and hematoxylin, and examined under a microscope.
Other tissues were compared to assess nonspecific uptake. Specific binding of
125I-labeled BB5-G1 to the human parathyroid was demonstrated; control human breast tumor
BT20 implants showed no uptake of the antibody. Clearance of the antibody was consistent
with the normal half life of IgGl.
Determination of Dose
[0054] Injections were made using 15 µg, 50 µg, or
150 pg of
125I-labeled BB5-G1 (activity) to 3 groups of 3 mice each, and the specific binding measured
by counting the radioactivity of various tissues after four days. The parathyroid
tissue showed 11%, 18%, and 7
% ID/gm for dose levels of 15µg, 50 µg, or 150 µg. respectively. Antibodies from all
three dosage levels remained in the blood after four days, but did not bind to other
tissues, as other tissues exhibited only background levels of radiation.
Time Dependence
[0055] The time course of labeling was determined by using 3 groups of 3 mice injected with
50
Ug of labeled antibody, sacrificing the animals at days 1, 4, and 7, and counting various
tissues, as described. There was a linear increase of binding to parathyroid with
time over this period reaching 26% ID/gm after 7 days, and the blood clearance was
determined to be consistent with this pattern. Highest levels of the antibody were
in the blood of animals sacrificed after 1 day, lowest in the blood of those sacrificed
at day 7.
Tissue Sections
[0056] Parathyroid grafts determined to contain antibody in the previous paragraphs were
excised with surrounding muscle and formalin-fixed, paraffin- embedded, and sectioned.
Slides were autoradiographed by dipping in a Kodak nuclear track emulsion exposed
for 14-21 days, developed and stained with hematoxylin. The presence of antibody was
shown by the appearance of silver grains over the cells. Figures 1 and 2 represent
bright field and dark field micrographs of the fixed tissue. The parathyroid tissue
is clearly defined by the antibody binding using either of these phases. The highest
degree of binding is to the periphery, away from the central fibrotic area.
Indium-111 Label
[0057] In addition, 4 mice administered 50 µg of In-labeled BB5-G1 were sacrificed on day
4 and tissues analyzed for % ID/gm. Parathyroid tissues showed a % ID/gm of almost
65%, whereas other tissues showed only nonspecific binding.
Example 6
Stimulation of Parathyroid Hormone Secretion
[0058] Bovine and human parathyroid cells were prepared by the collagenase/DNase method
of Brown. B.M., et al, (supra). Human cells were used the same day as acutely dispersed
cells; bovine cells either were used the same day or were cultured in suspension for
1-2 days in equal parts Hamm's F12 and Dulbecco's modified Eagle medium containing
4% calf serum and 5 ug/ml insulin, as described below.
[0059] In an initial experiment acutely dispersed bovine cells were treated with 5000 ng/ml
BB5-M monoclonal antibody at both high and low calcium concentrations and the secretion
of parathyroid hormone (PTH) was measured in units of ng PTH/10
5 cells/hr by radioimmunoassay using labeled anti-serum raised against the carboxy
terminal fragment of PTH containing amino acids 35-84. The antiserum thus detects
both intact PTH and the C-terminal fragment.
[0060] Table 1 shows the effect of 5000 ng/ml BB5-M on the secretion of PTH at high and
low calcium concentrations.
Table 1 shows that both at low and high calcium concentrations, BB5-M almost doubles
the level of secretion of PTH, while a control antibody, HPCµ2 has no detectable effect.
The values shown are the mean + SD for three separate cell preparations.
[0061] Similar results were obtained for acutely dispersed human parathyroid cells as shown
in Table 2. The dispersed human parathyroid preparations were subjected to 5000 ng/ml
BB5-M in the presence of 0.5 mM calcium ion and PTH secretion again expressed as ng
PTH/10
5 cells/hr.
[0062] Again a reproducible stimulation of PTH secretion occurs. -The values are for 5 replicate
incubations of the individual preparations.
[0063] Unlike B agonist drugs such as isoproteronol. the effect of BB5-M shows a linear
time dependence as illustrated in Figure 3. Acutely dispersed bovine cells in 0.5
mM calcium ion were treated with 5000 ng/ml BB5-M (or control cells were untreated)
and the supernatants were assayed for ng PTH per
105 cells as described above. After a 15 min lag time. the secretion curve for the BB5-M
treated cells diverges from that for controls to show the expected increased levels
of secretion. Thus, results as shown in Tables 1 and 2 can validly be based on hourly
secretion rate.
[0064] A dose response curve of the effect of BB5-M on PTH secretion was determined for
the acutely dispersed bovine cells, and for dispersed bovine cells after culturing
for 1 or 2 days to regenerate the surface markers. The results are shown in Figure
4. As expected, higher dosage levels of BB5-M are more effective in enhancing secretion
of PTH; in addition lower dosage levels are required for cultured cells which have
had the opportunity to generate the surface markers responsive to BB5-M. The effect
of BB5-M on dispersed cells was not apparent until a dosage level of
5 ug/ml was supplied; conversely, comparable effect on secretion of PTH from 2 day
cultured cells was obtained using a dosage of only 50 ng/ml; and for 1 day cultured
cells using 500 ng/ml. The results shown in Figure 4 are for 0.5 mM calcium ion concentration;
similar results were obtained but at 40% reduced PTH secretion levels, in the presence
of 2 mM calcium ion.
[0065] Further characterization of the nature of the stimulation was tested by examining
the effect of the antibody on cyclic AMP levels and on the nature of the PTH secreted.
[0066] Cyclic AMP was determined by extraction from cell pellets using 0.1 N HC1 and determining
cyclic AMP concentration in the extract by radioimmunoassay. The assay was performed
after acetylating both cyclic AMP standards and the extracts. The anti-sera used in
the assay were raised against acetylated cyclic AMP. Dispersed bovine parathyroid
cells in the presence of 0.5 mM calcium ion and with or without 5000 ng/ml B
B5-
M were assayed for cyclic AMP content at intervals up to 90 min after treatment with
BB5-M. The level of cyclic AMP in both control and BB5-M treated cells was approximately
400 fmoles/10
5 cells and remained unchanged over this time period.
[0067] In addition, the effect on the secretion level of the intact and the carboxy terminal
portion of the PTH was explored. Normally, at low calcium concentrations, the parathyroid
gland secretes about 50% of the PTH-synthesized as intact PTH and retains about 10%
of the PTH formed. 40% of the PTH synthesized is degraded and some is secreted as
the carboxy terminal portion of the peptide (amino acids 35-84).
[0068] Acutely dispersed bovine cells in 0.5 mM calcium ion were treated with 5000 ng/ml
BB5-M or untreated as controls and the supernatants were examined -after 1.5 hr using
polyacrylamide gel electrophoresis in 8 M urea, pH 4.5.
[0069] PTH protein was located on the segmented gel by radioimmunoprecipitation with anti-sera
raised against the C-terminal portion of PTH. The results are shown in Figure 5. It
is apparent that the stimulation effect of the BB5-M is directed specifically to the
intact protein; the level of C-terminal fragment secreted is not changed.